Surface mount light-emitting devices using light-emitting elements feature a small size, a good power efficiency, and light emission of brilliant color. The light-emitting elements eliminate the risk of lamp failures since they are semiconductor elements. They are also characterized by improved initial drive performance and resistance to vibration and repeated turn-on and off. Because of these improved properties, light-emitting devices using light-emitting elements such as light-emitting diodes (LED) and laser diodes (LD) are utilized as light sources in varying applications. Recently, light-emitting elements have marked a rapid advance toward higher outputs.
For the surface mount light-emitting devices, thermoplastic resins such as liquid crystal polymers, polyphenylene sulfide (PPS) and nylon are often used as molded parts due to ease of mass-scale production. On the other hand, epoxy resins are used in sealing members for protecting the light-emitting elements from moisture, dust and contaminants (see, for example, JP 3512732, JP-A 2001-234032, and JP-A 2002-302533). Also silicone resins are used as the output of light-emitting elements is increased.
However, prior art thermoplastic resins used as moldings in surface mount light-emitting devices are less resistant to light due to the inclusion of an aromatic component within the molecule although they are resistant to heat. Also, since hydroxyl groups or other groups for improving adhesion are absent at molecular ends, the resins exhibit poor adhesion to leads and sealing members. In particular, sealing members using silicone resins lack long-term reliability since they show a drastic drop in adhesion to molded parts using thermoplastic resins, as compared with sealing members using epoxy resins. Epoxy resins are used as sealing members, but not as molded parts in leadframe type surface mount devices because of their difficulty to mold.
Besides, light-emitting elements of gallium nitride compound semiconductor capable of blue emission produce higher outputs than light-emitting elements capable of red emission and also generate more amounts of heat. Thus, degradation of molded parts becomes a problem when light-emitting elements of blue emission are used.
Also, JP 2656336 describes an optical semiconductor device wherein an encapsulating resin is a cured product of a B-staged epoxy resin composition for optical semiconductor encapsulation comprising an epoxy resin, a curing agent, and a cure accelerator, wherein the constituent components are uniformly mixed at a molecular level. It is described that the epoxy resin used herein is typically a bisphenol A epoxy resin or bisphenol F epoxy resin, and triglycidyl isocyanate or the like may also be used. In Example, triglycidyl isocyanate is used and added in a small amount to a bisphenol type epoxy resin. As long as the present inventors have empirically studied, the B-staged epoxy resin composition for semiconductor encapsulation suffers from a problem of yellowing during long-term holding at high temperatures.
JP 2656336 describes: “The epoxy resin composition for optical semiconductor encapsulation is advantageously used as encapsulants for light-sensing elements in compact disc players, line sensors and area sensors which are solid-state image sensors. Optical semiconductor devices in which light-sensing elements such as solid-state image sensors are encapsulated with such epoxy resin compositions for optical semiconductor encapsulation are high-performance products which form images free of fringes caused by optical variations of the resin or black peppers caused by foreign particles in the encapsulating resin. Despite resin encapsulation, they exhibit at least equivalent performance to ceramic packages.” It is thus understood that the encapsulating resin of this patent is used with light-sensing elements, but not for the encapsulation of light-emitting elements.
In this regard, JP-A 2000-196151, JP-A 2003-224305 and JP-A 2005-306952 refer to the use of triazine derived epoxy resins in epoxy resin compositions for the encapsulation of light-emitting elements. These epoxy resins, however, are not solid materials obtained by reacting a triazine derived epoxy resin with an acid anhydride.
Known references relating to the present invention include the foregoing as well as JP-A 2005-259972, JP-A 2006-156704, and Electronics Mount Technology, April 2004.